1. Field of the Invention:
This invention relates to high capacity hybrid ion exchange material with enhanced ability to selectively remove molecular (organics) and anionic (fluoride ion and oxyanions of phosphorus and arsenic) species from drinking water, industrial streams, and wastes, for applications predominantly in the medical and food industries.
2. Description of Related Art:
Activated carbon has been widely used in different water treatment applications for decades. For example, activated carbon is present in home water purification systems due to the ability to remove efficiently volatile organic compounds, pesticides, chlorine, odor, and bad taste. Adsorption performance of activated carbon, capacity, and selectivity, depend on various factors. The most critical parameters include: a) surface area that can vary from 600 m2/g up to 2000 m2/g; b) total pore volume that can vary from 0.5 cm3/g up to 1.5 cm3/g; and, c) pore size distribution.
Microporous activated carbons with pore size less than 2 nm exhibit high affinity towards small organic molecules, and volatile organic compounds such as chloroform; however, due to size exclusive mechanisms they do not adsorb larger organic compounds. Mesoporous activated carbons with pore size from 2 nm to 50 nm exhibit a high affinity towards large organic molecules such as pesticides and herbicides, as well as to colloidal particles, including colloidal particles of lead.
A positively charged surface of activated carbons affords weak anion exchangers that are able to adsorb some anions, including oxyanions of arsenic. Anion exchange capacity of activated carbons is extremely small in comparison with polyvalent metal (Fe, Ti, Zr, etc.) hydrous oxides used for selective removal of As, P, V, Sb, Cr, Se, etc., anions from different aqueous streams (see, e.g., C. B. Amphlett, Inorganic Ion Exchangers, Elsevier, New York (1964)).
In order to improve the anion-exchange function of activated carbons, impregnation with different polyvalent metal hydrous oxides has been proposed and implemented, which results in the formation of composite ion exchange materials. Different types of active carbon ranging from powders to granular, from micro- to meso-porous, as well as variety of impregnation techniques (impregnation using excess of metal containing solution, incipient wetness, chemical vapor deposition, etc.), have been tried for addition of an active inorganic component. Furthermore, hydrous oxides of Fe, Zr, Ti, Al, etc., have been tried as doping active media (see, e.g., U.S. Pat. Nos. 4,178,270 ; 4,692,431; 5,277,931 ;5,948,265 ; 6,914,034; 7,378,372; 7,429,551 ; 7,572,380; 8,178,065; 8,242,051; U.S. Patent Publication No. 2014/0021139; GB 1581993; and, EP 0815939).
In general, anion exchange properties of composite materials depend on the type of impregnated oxide chosen, and as a rule capacity increases up to a certain point with an increase of inorganic oxide content; however, the correlation between the amount of dopant oxide and capacity is not universal, as in many cases capacity is a function of a specific metal oxide phase/structure formed in the pores and it can vary significantly for similar loadings of the same polyvalent metal oxide. Moreover, as the active metal oxide component is deposited in the pores of activated carbon carrier, the high values of loading result in blocking the activated carbon pores, thus reducing its efficiency for removal of organic molecules. In other words, an attempt to increase ion exchange capacity of composite adsorbent above a maximum point is accompanied by a decrease in capacity towards organics. Preferred loading of polyvalent metal oxide 10 wt % to 20 wt % has been empirically shown to provide composite media the ability to remove efficiently both organic and inorganic species; but, even highest possible loadings do not produce adsorbents with ion exchange capacity close or equal to that of individual polyvalent metal hydrous oxide used as dopants.